Hot water heaters for heating potable water for use in cooking, showers, baths and the like, and which potable water heaters are used in recreational vehicles, boats, motor homes and other vehicles are, of course, well known. The fuel typically used in such heaters is electric power or propane. The disadvantages in using propane are well known since propane is maintained in its liquid state by a pressurized storage vessel. In a boat, the gas, being heavier than air, will accumulate in the lower portions of the boat in the event there is a leak. The fuel is volatile and if it is ignited, an explosion may occur. More mundane considerations include the fact that propane fuel is not readily available. Statutes and local regulations may require that such fuels be stored under stringent conditions and commercial outlets are therefore not always at hand.
Yet a further consideration is the efficiency of the potable water heater itself. In a boat or vehicle, the space available for a water heater is at a premium. It is desirable to have the water heater take up a relatively small volume.